Quick-EXAFS monochromator

Expected flux at the focusing point

The SOLEIL designed Quick-EXAFS monochromators are made of two independent channel-cut crystals (Si(111) and Si(220)) and was first used on SAMBA beamline. Each channel-cut crystal is mounted on a cam driven tilt table allowing it to oscillate periodically with amplitude θ(t) around an average fixed Bragg angle θB. The amplitude can be tune from 0.1 to 4° by an original SOLEIL in vacuum variable cam design. The θB Bragg angle is selected by one of the two goniometers holding the oscillating tilt tables. The 4.5 to 40 keV energy range is available using both Quick-EXAFS monochromators. The channel-cut crystal can be changed by the other one in few seconds during an experiment allowing to record quick-EXAFS data at absorption edges very far in energy. For instance the XAS study of a bimetallic catalyst at both edges during the same catalytic reaction is now possible with the SAMBA’s QuEXAFS set-up, even if the edge energies of those elements are covered by two distinct crystals.

Quick-exafs monochromator

Maximum performance of the Quick-EXAFS mechanics in terms of oscillation frequency of the channel-cut is 40 Hz for two recorded spectra: one with the Bragg angle collection in the downward direction and the other with the Bragg angle collection in the upward direction. Due to the photon flux available at the sample position at the SAMBA beamline in QuEXAFS configuration ((flux ~ 1011 ph/s at 8 keV) the optimal time resolution of experiments on real concentrated and not too absorbing samples is around 100 ms. On ROCK we expect to reach 1012 ph/s in 50 ms.

(left) Absorption of stacked Cr and Mn metallic foils measured over an amplitude of 3.6 °. Data are the average of 10 spectra each collected at 1Hz. (right) k2 weighted Quick-EXAFS are compared to standard scans taken in almost 15 min.

Cabane EXAFS

Transmission

Oken ionization chambers

Fluorescence APD ou PIPS

Avalanche Photo Diode (APD)

PIPS

Edge Jump

Large energie range from 4 keV (Si111) to 37 keV (Si311) in 30s
The remote selection of the monochromator crystals, Si(111) or Si(311), allowing users to permanently access energies between 4 and 37 keV in Quick-exafs mode.

Cellules liquides

We have different cells with fixed or variable optical path available for basic or acidic solution. Two of them are thermostatically controlled. Note Kapton, Mylar, PP or PTFE can be used as windows depending of the nature of the solution.

Préparation des échantillons

Gaz

The application for the use of specialty gases must be stipulated in your proposal in order that the security service can assess the associated risks. Specialty gases must be commanded 8 weeks before your experiment, also you have to prevent your local contact well in advance, for common gases (helium, argon, nitrogen, hydrogen, air and oxygen) only 2 weeks are sufficient.

Helium liquid

The application for the use of helium liquid must be stipulated in your proposal and recalled to your local contact in such a way to order sufficiently in advance the suitable volume.